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AlAsSb quantum wells grown by molecular beam epitaxy
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Physica E 17 (2003) 201 – 203 www.elsevier.com/locate/physe
Strong carrier localization in Sb-terminated InGaAs/AlAsSb quantum wells grown by molecular beam epitaxy T. Mozume∗ FESTA Laboratories, Femtosecond Technology Research Association, 5-5 Tokodai, Tsukuba 300-2635, Japan
Abstract We report here on a study of the photoluminescence (PL) and photore.ectance (PR) spectra from InGaAs/AlAsSb multiple quantum wells with antimony interface terminations that were grown by molecular beam epitaxy. The PL spectrum exhibits a broad peak between 4 and 300 K, composed of interface-related transitions and transitions between con4ned energy levels in the well (EC ). Features of the quantum well related interband transitions (En Hm ) are clearly observed in the PR spectra between 55 and 300 K. Below 150 K, EC shifts signi4cantly toward lower energy from E1 H1 , indicating strong carrier localization. ? 2002 Elsevier Science B.V. All rights reserved. Keywords: InGaAs/AlAsSb; Quantum wells; Photoluminescence; Photore.ectance; Carrier localization
1. Introduction In0:53 Ga0:47 As=AlAs0:56 Sb0:44 quantum wells (QWs) lattice-matched to InP substrates are recently attracting much attention for optical and electrical devices, because of their very large conduction band o=sets of 1:6 eV [1]. We have reported on the near-infrared intersubband transitions [2] and ultra-fast absorption response of 685 fs [3] at 1:55 m for this material system, demonstrating that it is well suited for the ultra high-speed optical devices used in optical communications networks. However, despite the potential applications of these novel quantum structures, very few studies have been reported on
AlAsSb systems, due to the diGculties involved in growing the AlAsSb, which includes two group-V elements, and has a large miscibility gap. We previously reported that the interface termination procedure has a profound in.uence on the QW properties of InGaAs/AlAsSb. The photoluminescence (PL) spectra of Sb-terminated InGaAs/AlAsSb MQWs are broadened and red-shifted, more so than those of the equivalent As-terminated version [4], indicating graded or disordered interfaces. This paper reports the detailed study of the e=ects of interface Sb-termination on the optical properties of 10-nm InGaAs/AlAsSb QWs using the PL and photore.ectance (PR). 2. Results and discussion
∗
Corresponding author. Tel.: +81-298-47-5181; fax: +81-29847-4417. E-mail address: [email protected] (T. Mozume).
An undoped 10 period InGaAs/AlAsSb multiple quantum wells (MQWs) with 10 nm AlAsSb barriers
1386-9477/03/$ - see front matter ? 2002 Elsevier Science B.V. All rights reserved. doi:10.1016/S1386-9477(02)00768-3
202
T. Mozume / Physica E 17 (2003) 201 – 203
0.88
300K
150 K 120 K 100 K 77 K 55 K 20 K 8K 0.7
(a)
0.8 0.9 1.0 energy (eV)
150K 125K 100K 77K
PL peak energy (eV)
200 K
∆R/R (arb. units)
PL intensity (arb. units)
250 K
PR Sb-term PL PR As-term fit
200K
300 K
0.86 0.84 0.82 0.80
55K (b)
0.7 0.8 0.9 1.0 1.1 1.2 energy (eV)
Fig. 1. Temperature dependence of the PL (a) and PR (b) spectra of Sb-terminated InGaAs/AlAsSb MQWs.
and 10 nm InGaAs wells was grown on an Fe-doped (0 0 1) InP substrate by conventional molecular beam epitaxy (MBE). The interfaces were terminated by antimony. Details of the MBE procedures are reported in Ref. [4]. PL and PR measurements were carried out between 4 K and room temperature. Temperature dependent PL spectra taken at around 10 W=cm2 and PR spectra are shown in Fig. 1. The PL spectra of the Sb-terminated QW show strong broadening and also show excitation power dependence (not shown) over the whole temperature range. The PL spectra can be 4tted by two or three Gaussian peaks (Fig. 2 of Ref. [5]). These peaks can be attributed to interface related transitions and a transition between con4ned energy levels in the well (EC ) [5]. Features of the interband transitions in the QWs are clearly observed in the PR spectra. The PR spectra exhibit 4rst-derivative-like features above 77 K and critical point energies are obtained through a nonlinear 4t with a 4rst derivative functional form of the unperturbed dielectric function. Above 150 K, EC corresponds well with the main transition energy (E1 H1 ) determined from the PR spectra (Fig. 2). The PR critical point energies coincide with the theoretical transition energies of QWs based on the envelope-function approach. The E1 H1 energy dependence on temperature exhibits typical behavior that can be 4tted by the empirical equation proposed by Varshni: Eg = E0 − T 2 =( + T ), where E0 = 0:869 eV, = 3:3 ×
0.78 0
50
100 150 200 250 300 temperature (K)
Fig. 2. Temperature dependence of the peak energy of the PL peak corresponding to transitions to con4ned subband levels, and also the PR critical point energies for the E1 H1 transition for Sb-terminated InGaAs/AlAsSb MQWs. The solid line is a least-squares 4t. The E1 H1 transition energies for As-terminated QWs are also shown.
10−4 eV=K and = 81:6 K (solid line in Fig. 2). As shown in Fig. 2, the E1 H1 energy corresponds well with that of As-terminated MQWs with same structure over the whole temperature range. As the temperature decreases from 150 to 8 K, the energy shift between EC and E1 H1 increases to about 20 meV, showing that the PL emission (EC ) at low temperature arises from levels well below E1 H1 . This quenching of EC is typical of strong localization e=ects. 3. Summary Temperature dependent PL and PR study of 10 nm InGaAs/AlAsSb MQWs grown by MBE with Sb interface terminations is reported. From the large red shift observed in the PL transition energy compared to the PR critical point energy, the occurrence of strong carrier localizaton is con4rmed, especially below 100 K. Acknowledgements This work was supported by the New Energy and Industrial Technology Development Organization
T. Mozume / Physica E 17 (2003) 201 – 203
(NEDO) within the framework of the Femtosecond Technology Project. References [1] N. Georgiev, T. Mozume, J. Appl. Phys. 89 (2001) 1064. [2] T. Mozume, et al., Inst. Phys. Conf. Ser. 162 (1999) 131.
203
[3] T. Akiyama, et al., Electron. Lett. 37 (2001) 129. [4] N. Georgiev, T. Mozume, J. Crystal Growth 209 (2000) 247. [5] T. Mozume, N. Georgiev, Physica E 13 (2002) 361.
Physica E 17 (2003) 201 – 203 www.elsevier.com/locate/physe
Strong carrier localization in Sb-terminated InGaAs/AlAsSb quantum wells grown by molecular beam epitaxy T. Mozume∗ FESTA Laboratories, Femtosecond Technology Research Association, 5-5 Tokodai, Tsukuba 300-2635, Japan
Abstract We report here on a study of the photoluminescence (PL) and photore.ectance (PR) spectra from InGaAs/AlAsSb multiple quantum wells with antimony interface terminations that were grown by molecular beam epitaxy. The PL spectrum exhibits a broad peak between 4 and 300 K, composed of interface-related transitions and transitions between con4ned energy levels in the well (EC ). Features of the quantum well related interband transitions (En Hm ) are clearly observed in the PR spectra between 55 and 300 K. Below 150 K, EC shifts signi4cantly toward lower energy from E1 H1 , indicating strong carrier localization. ? 2002 Elsevier Science B.V. All rights reserved. Keywords: InGaAs/AlAsSb; Quantum wells; Photoluminescence; Photore.ectance; Carrier localization
1. Introduction In0:53 Ga0:47 As=AlAs0:56 Sb0:44 quantum wells (QWs) lattice-matched to InP substrates are recently attracting much attention for optical and electrical devices, because of their very large conduction band o=sets of 1:6 eV [1]. We have reported on the near-infrared intersubband transitions [2] and ultra-fast absorption response of 685 fs [3] at 1:55 m for this material system, demonstrating that it is well suited for the ultra high-speed optical devices used in optical communications networks. However, despite the potential applications of these novel quantum structures, very few studies have been reported on
AlAsSb systems, due to the diGculties involved in growing the AlAsSb, which includes two group-V elements, and has a large miscibility gap. We previously reported that the interface termination procedure has a profound in.uence on the QW properties of InGaAs/AlAsSb. The photoluminescence (PL) spectra of Sb-terminated InGaAs/AlAsSb MQWs are broadened and red-shifted, more so than those of the equivalent As-terminated version [4], indicating graded or disordered interfaces. This paper reports the detailed study of the e=ects of interface Sb-termination on the optical properties of 10-nm InGaAs/AlAsSb QWs using the PL and photore.ectance (PR). 2. Results and discussion
∗
Corresponding author. Tel.: +81-298-47-5181; fax: +81-29847-4417. E-mail address: [email protected] (T. Mozume).
An undoped 10 period InGaAs/AlAsSb multiple quantum wells (MQWs) with 10 nm AlAsSb barriers
1386-9477/03/$ - see front matter ? 2002 Elsevier Science B.V. All rights reserved. doi:10.1016/S1386-9477(02)00768-3
202
T. Mozume / Physica E 17 (2003) 201 – 203
0.88
300K
150 K 120 K 100 K 77 K 55 K 20 K 8K 0.7
(a)
0.8 0.9 1.0 energy (eV)
150K 125K 100K 77K
PL peak energy (eV)
200 K
∆R/R (arb. units)
PL intensity (arb. units)
250 K
PR Sb-term PL PR As-term fit
200K
300 K
0.86 0.84 0.82 0.80
55K (b)
0.7 0.8 0.9 1.0 1.1 1.2 energy (eV)
Fig. 1. Temperature dependence of the PL (a) and PR (b) spectra of Sb-terminated InGaAs/AlAsSb MQWs.
and 10 nm InGaAs wells was grown on an Fe-doped (0 0 1) InP substrate by conventional molecular beam epitaxy (MBE). The interfaces were terminated by antimony. Details of the MBE procedures are reported in Ref. [4]. PL and PR measurements were carried out between 4 K and room temperature. Temperature dependent PL spectra taken at around 10 W=cm2 and PR spectra are shown in Fig. 1. The PL spectra of the Sb-terminated QW show strong broadening and also show excitation power dependence (not shown) over the whole temperature range. The PL spectra can be 4tted by two or three Gaussian peaks (Fig. 2 of Ref. [5]). These peaks can be attributed to interface related transitions and a transition between con4ned energy levels in the well (EC ) [5]. Features of the interband transitions in the QWs are clearly observed in the PR spectra. The PR spectra exhibit 4rst-derivative-like features above 77 K and critical point energies are obtained through a nonlinear 4t with a 4rst derivative functional form of the unperturbed dielectric function. Above 150 K, EC corresponds well with the main transition energy (E1 H1 ) determined from the PR spectra (Fig. 2). The PR critical point energies coincide with the theoretical transition energies of QWs based on the envelope-function approach. The E1 H1 energy dependence on temperature exhibits typical behavior that can be 4tted by the empirical equation proposed by Varshni: Eg = E0 − T 2 =( + T ), where E0 = 0:869 eV, = 3:3 ×
0.78 0
50
100 150 200 250 300 temperature (K)
Fig. 2. Temperature dependence of the peak energy of the PL peak corresponding to transitions to con4ned subband levels, and also the PR critical point energies for the E1 H1 transition for Sb-terminated InGaAs/AlAsSb MQWs. The solid line is a least-squares 4t. The E1 H1 transition energies for As-terminated QWs are also shown.
10−4 eV=K and = 81:6 K (solid line in Fig. 2). As shown in Fig. 2, the E1 H1 energy corresponds well with that of As-terminated MQWs with same structure over the whole temperature range. As the temperature decreases from 150 to 8 K, the energy shift between EC and E1 H1 increases to about 20 meV, showing that the PL emission (EC ) at low temperature arises from levels well below E1 H1 . This quenching of EC is typical of strong localization e=ects. 3. Summary Temperature dependent PL and PR study of 10 nm InGaAs/AlAsSb MQWs grown by MBE with Sb interface terminations is reported. From the large red shift observed in the PL transition energy compared to the PR critical point energy, the occurrence of strong carrier localizaton is con4rmed, especially below 100 K. Acknowledgements This work was supported by the New Energy and Industrial Technology Development Organization
T. Mozume / Physica E 17 (2003) 201 – 203
(NEDO) within the framework of the Femtosecond Technology Project. References [1] N. Georgiev, T. Mozume, J. Appl. Phys. 89 (2001) 1064. [2] T. Mozume, et al., Inst. Phys. Conf. Ser. 162 (1999) 131.
203
[3] T. Akiyama, et al., Electron. Lett. 37 (2001) 129. [4] N. Georgiev, T. Mozume, J. Crystal Growth 209 (2000) 247. [5] T. Mozume, N. Georgiev, Physica E 13 (2002) 361.